Hot-blast cupola furnace

ABSTRACT

A hot-blast cupola furnace with a liningless stack having a water-cooled jacket and a hearth with a refractory lining below the level of the tuyeres of the furnace is provided with an inclined hearth bottom which is connected through separate channels to at least two pressure siphons at a lower level than the hearth bottom and the tuyeres are provided with cooling means which are arranged to cool the upper parts of the tuyeres more vigorously than the lower parts. This furnace is operated with an acid slag and at such a rate that from 8 to 15 metric tons of melt is produced per hour per square meter of hearth area. Both the iron and the slag produced are continuously tapped from the hearth and are run into one of the pressure siphons where they are allowed to react together.

United States Patent m t e m a C m 0 4 9 .1 l 7 6 8 9 0 2 Dusseldorf, Germany [2]] Appl. No. 746,047 [22] Filed [72] Inventor Siegfried Tunder July 19, 1968 FOREIGN PATENTS 141,956 4/1920 Great Britain................ 1,135,617

Primary Examiner-Gerald A. Dost [45] Patented Aug. 17,1971 [73] Assignee Gesellschaft fur I-Iuttenween m.b.II.

8/1962 Germanym... Dusseldorf, Germany Dec. 6, 1967 Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Germany [32] Priority 1 Lerner and Daniel J. Tick :[31] P15834523 54 HOT.BLAST CUPOLA FURNACE ABSTRACT: A hot-blast cupola furnace with a liningless stack having a water-cooled jacket and a hearth with a refractory lining below the level of the tuyeres of the furnace is vided with an inclined hearth bottom which is conne 9 Claims, 8 Drawing Figs.

pro-

266/25, cted 266/39 266/41 through separate channels to at least two pressure siphons at a C21b7/00 lower level than the hearth bottom and the tuyeres are pro- 266/3134 vided with cooling means which are arranged to cool the 75/43, 110/1825, 122/66 51 so 41, 2s, 38; 122/66; 110/1325; 75 41,43, 46

upper parts of the tuyeres more vigorously than the lower parts. This furnace is operated with an acid slag and at such a [56] References Cited UNITED STATES PATENTS 5/1882 Gordon........................ 8/1934 Fox et a1.

rate that from 8 to 15 metric tons of melt is produced per hour per square meter of hearth area. Both the iron and the slag produced are continuously tapped from the hearth and are run into one of the pressure siphons where they are allowed to react together.

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SHEET '4 [IF 4 INVEN TOR 1 Lulu? HOT-BLAST (JUPOLA Ace This invention relates to a method of operating continuously tapped, hot-blast cupola furnaces with liningless stacks having water-cooled jackets and hearths lined with refractory material, and also relates to cupola furnaces for use in carrying out the method.

Such cupola furnaces are described for example in German Pat. No. 1,171,564 according to which a hot-blast cupola furnace has a liningless stack consisting of a steel plate jacket cooled from the outside by a spray of water. The hearth and the bosh are lined with a refractory lining, because during the smelting a pool of liquid iron together with a considerable amount of slag collects in the hearth. The wall of the hearth is equipped with a number of water-cooled tuyeres, distributed evenly around the circumference. From German Pat. No. 1,217,027 a hot-blast cupola furnace which is continuously tapped is also known. To the inclined bottom of the furnace there is connected a forehearth, situated at a lower level, in which the iron is separated from the slag. The forehearth has a siphon through which the molten iron runs out, and next to this, displaced towards the side, there is an overflow for slag. Finally, from German Pat. No. 1,061,038 a hot-blast cupola furnace is known the hearth of which has at least two siphons at tap hole level, which are operated alternately. The arrangement allows iron and slag to be drawn off separately, allowing the furnace itself to be operated continuously. While one siphon is being repaired, the liquids are drawn off through the other siphon.

However, all known continuously tapped hot-blast cupola furnaces have this in common, that they operate only with basic slags. This is a considerable disadvantage, because many kinds of cast iron, for example grey cast iron and malleable cast iron, cannot be smelted with a basic slag. The consequence is that these kinds of cast iron are still today smelted in discontinuously functioning cupola furnaces containing acid slags. It is only by using an acid slag that it is possible to obtain reliably the necessary carbon, silicon and manganese contents in the iron. Acid slag smelting has therefore hitherto required the use of two cupola furnaces, a continuous smelting process being achieved by alternately tapping the two furnaces. The basic, liningless and water-cooled hot-blast cupola furnace therefore has the advantage that a single furnace can produce an uninterrupted flow of melt. The smelting proceeds continuously until interrupted by a general shutdown, for example during holidays, and during these pauses it is merely necessary to steam the cupola furnace.

In the basic process, although the hot-blast cupola furnace is mainly liningless, cooled on the outside by water, the tuyeres in the wall of the hearth are not damaged, because their upper surfaces are protected by a coating of solidified slag, which is formed in the region above the tuyeres due to the high melting point of the basic slag. The hearth is also protected in this way. These parts are also not very greatly stressed, because the output of melt is comparatively low, being for example between 5.5 and 6.5 metric tons per house per square meter of hearth area due to the high proportion of coke. A basic hot-blast cupola furnace can therefore be operated using the customary copper tuyeres, equipped with water inlets and outlets.

The usual kind of hot-blast cupola furnace has a slag siphon which functions on the principle of communicating tubes connected to the hearth, to the effect that there is always a pool of molten iron, covered by a slag layer between 30 and 50 cm. deep, in the hearth. This slag serves to remove oxygen and sulfur from the droplets of molten iron sinking through it. The basic slag contains hardly any iron oxides, and the hearth under the tuyeres, that is to say in the region of the pool of iron, can be lined with carbon bricks or a tamped composition or both. The slag does not attack this lining. The lining of the hearth is subjected to a certain amount of mechanical abrasion, due to the movement of the iron and slag, but this mflres it necessary for the furnace to be shut down only after two or three months of operation.

Nevertheless, although the basic hot-blast cupola furnace does have these advantages, it suffers from a limitation, in that it cannot be used for smelting those kinds of cast iron, for example grey cast iron and malleable cast iron, in which the carbon and silicon must be present in precise contents. The reasons are as follows: A basic slag neutralizes the cellular structure of the coke ash, whereas an acid slag does not do this. The neutralization of the coke ash activates the carbon in the coke, which carburizes the iron. The carburizing thus depends on the basicity of the slag. This basicity varies considerably and consequently the degree of carburizing applied to the iron cannot be effectively controlled in practice. A further instability in the process is brought about by temperature variations, which cause fluctuations in the oxidization of the silicon. The silicon concentration in the iron therefore varies, as also does the silica concentration in the slag, and this again changes the basicity of the slag, and therefore the concentration of carbon in the iron.

The object of the present invention is to avoid these difficulties, and in particular to develop the operation of a continuously tapped hot-blast cupola furnace in such a way that iron can be produced in which the carbon and silicon contents are precisely as specified, and constant.

To this end, according to this invention a continuously tapped, hot-blast cupola furnace with a liningless stack having a water-cooled jacket and a hearth lined with refractory material is operated by a method in which an acid slag is used and from 8 to 15 metric tons of melt is produced per hour per square meter of hearth area, the iron being continuously tapped with the slag from the hearth, and the iron and slag being allowed to react together in a pressure siphon located away from the hearth.

The output of melt is considerably increased by the method in accordance with the invention, due to the use of an acid slag, and this increases the stressing of the water-cooled tuyeres. Furthermore the tuyeres are not protected by a covering of slag, because the acid slag has a comparatively low melting point. It is therefore preferable to supply to each tuyere a flow of water which is at least 15 m. /h., the cooling water being preferably directed towards the most highly stressed part, that is the upper part, of the tuyere.

The method is best carried out in a hot-blast cupola furnace with a liningless stack having a water-cooled jacket and a hearth with a refractory lining below the level of the tuyeres, wherein, in accordance with the invention, the hearth bottom is inclined and is connected through separate channels to at least two pressure siphons at a lower level than the hearth bottom, and the tuyeres have cooling means which are arranged to cool the upper parts of the tuyeres more vigorously than the lower parts.

The sloping bottom of the furnace allows the iron and the acid slag to run off continuously, that is to say to drain out of the hearth continuously, to the effect that the oxides in the slag hardly have time to attack the lining of the hearth. The iron and the slag run off through one of the connecting channels and collect in a pressure siphon, which is situated at a lower level than the furnace bottom. The iron and the slag are drawn off continuously from the pressure siphon. The reaction between the iron and the slag takes place essentially outside the cupola furnace, the iron flowing through the connecting channel into the pool of slag floating on the molten iron in the pressure siphon. The iron penetrates downwards through the layers of slag. The pressure siphons are preferably closed by gastight covers.

The method in accordance with the invention can therefore be conducted in such a way that cupola furnace gas is present constantly both in the upper part of the pressure siphon and in the connecting channels. The pressure siphon is therefore always under the same gas pressure as the cupola furnace. The attack of the acid slag on the refractory lining of the pressure siphon is easily dealt with by providing two siphons. To repair a siphon it is merely necessary to block up its connecting channel. This siphon can then be repaired, while iron and slag leave the furnace through the other pressure siphon.

The necessary more vigorous cooling of the upper parts of the tuyeres can be obtained by providing each tuyere with a double-walled blast nozzle the upper part of which contains cooling water supply pipes which terminate near the blast nozzle tip. Preferably, the outlets of the cooling water pipes are directed towards the outer wall of the nozzle. The upper part of each blast nozzle preferably contains four cooling water inlet pipes alternating with outlet pipes. Alternatively a good cooling effect is obtained by subdividing each blast nozzle by axially extending walls into guiding ducts which are connected together near the tip of the blast nozzle by an annular chamber. Each tuyere preferably then has an annular water distributor chamber having at its top an outlet chamber connected to an outlet pipe and also connected through a passage to one of the guiding ducts. In this way, the entire supply of cooling water is concentrated into the upper part of the tip of the blast noale and compelled to flow away from here through the single outlet chamber.

An example of a method and of a furnace for carrying out this method in accordance with the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a vertical longitudinal section through a tuyere of the furnace;

FIG. 2 is a front view of the tuyere shown in FIG. 1;

FIG. 3 shows an alternative tuyere construction;

FIG. 4 is a front view of the tuyere shown in FIG. 3;

FIG. 5 is a cross section on the line V-V in FIG. 3;

FIG. 6 is a cross section on the line VI-Vl in FIG. 3;

FIG. 7 is a vertical longitudinal section through the hearth of the furnace which has a pressure siphon; and

FIG. 8 is a horizontal section through the furnace hearth shown in FIG. 7.

The tuyere shown in FIGS. 1 and 2 comprises a ring which is inserted in the wall of the furnace hearth and is connected to a feed pipe, not shown in the drawing, which supplies a blast of hot air. The ring 15 supports a double-walled tuyere nozzle 16, the inner wall 17 of which is in contact with the hot blast and the outer wall 18 of which is in contact with the glowing coke, the liquid iron and the falling drops of slag. In order to obtain the amount of cooling made necessary by the high throughout or flow-through rate of the melt in the furnace and the high thermal stresses, the upper half of the tuyere contains four water inlet pipes 19 which extend inwards to near the tip of the blast nozzle. The outer wall 18 is stressed considerably more than the inner wall 17 and for this reason the outlets 21 of the water inlet pipes 19 are directed outwards towards the inner surface of the outer wall 18, so that cooling water impinges directly on the outer wall. The water leaves through water outlet pipes 22 located between the inlet pipes 19. The tuyere also has a further connection 23 for draining the residual cooling water from the tuyere when the furnace is shut down for repair.

In the case of the tuyere shown in FIGS. 3 to 6, the cooling efiect required for the method in accordance with the invention is obtained by positively controlling the path of the cooling water by means of guiding ducts leading to an annular duct near the tip of the blast nozzle. This tuyere comprises a ring 25, which is inserted into the wall of the furnace hearth. The ring is hollow and contains a distribution chamber 26 to which is connected a water inlet pipe 27. On either side of a water outlet pipe 28 there are walls 29, 30 forming between them a water outlet chamber 31, which is connected to the hollow interior of a blast nozzle 33 through a passage 32 in the form of a slot. The blast nozzle 33 is itself subdivided into separate passages 37 by walls 36. Each passage 37 is connected by a passage 38 to the distribution chamber 26. The separating walls 36 do not extend all the way to the tip of the nozzle, but stop short to leave an annular chamber 39, which connects together the individual passages 37. When the cupola furnace is shut down for repairs, the residual water remaining in the tuyere is drained away through a branch pipe 30 of the water inlet pipe 27 In FIGS. 7 and 8 the furnace hearth is shown with two pressure siphons. The method in accordance with the invention allows steady, or nearly constant, carbon and silicon contents to be obtained in the iron in the presence of an acid slag. The carbon content in the iron is determined by the height of the bed of glowing coke in the carburizing zone under the tuyeres 41. This height is the vertical distance between the horizontal plane containing the tuyeres, and the furnace bottom 42, and can be varied to suit operational requirements by adjusting the level to which the lining is tamped. If the furnace bottom is at a low level the carbon concentration in the iron will be high, whereas a high furnace bottom results in a low concentration of carbon in the iron. In the method in accordance with the invention the molten iron and slag are not allowed to remain as a pool in the hearth of the furnace, but are continuously run off over the inclined furnace bottom 42 and through a channel 43 into a pressure siphon 44. In the pressure siphon the iron separates from the slag and the two liquids flow continuously out of the pressure siphon, the iron flowing out through a siphon outlet leading to a channel 45, and the slag flowing out through a siphon leading to a slag channel 46. The pressure siphon is closed by a cover 47, which makes a good seal, so that the same gas pressure prevails in the cupola furnace and in the pressure siphon.

I claim:

1. In a continuously tapped, acidically operated hot-blast cupola furnace including a liningless stack, a water-cooled jacket surrounding said stack, tuyeres at the bottom of said stack, a hearth below the level of said tuyeres and a refractory lining in said hearth, the improvement comprising an inclined bottom in said hearth, at least two pressure siphons at a lower level than said bottom, means defining separate channels interconnecting said hearth and said pressure siphons, and means for cooling said tuyeres, said cooling means comprising double-walled blast nozzles and coolant conducting means therewithin arranged to cool upper parts of said tuyeres more vigorously than lower parts thereof.

2. A furnace as claimed in claim 1, further comprising a cover gastightly sealing each of said pressure siphons.

3. A furnace as claimed in claim 1, wherein each tuyere is provided with one of said double-walled blast nozzles, a tip on said nozzle, cooling water supply pipes extending within the upper part of said nozzle and an outlet portion on each of said cooling water supply pipes, said outlet portions being adjacent said tip.

4. A furnace as claimed in claim 3, wherein said outlet portions are directed outwards within said nozzle.

5. A furnace as claimed in claim 3, wherein said nozzle contains four of said cooling water supply pipes and further comprising water outlet pipes interposed between said supply pipes.

6. In a hot-blast cupola furnace including a liningless stack, a water-cooled jacket surrounding said stack, tuyeres at the bottom of said stack, a hearth below the level of said tuyeres and a refractory lining in said hearth, the improvement comprising an inclined bottom in said hearth, at least two pressure siphons at a lower level than said bottom, means defining separate channels communicating said hearth with said pressure siphons and means for cooling said tuyeres, said cooling means being arranged to cool upper parts of said tuyeres more vigorously than lower parts thereof, each of said tuyeres including a double-walled blast nozzle, a tip on said nozzle, axially extending walls within said nozzle subdividing said nozzle into guide ducts and means defining a passage within said tip interconnecting said guide ducts.

7. A furnace as claimed in claim 6, further comprising means in each of said tuyeres defining an annular water distributor chamber, said chamber including means defining an outlet chamber at the top thereof, a water outlet pipe communicating with said outlet chamber and means within said 3,599,950 p g 6 tuyere defining a passage communicating said outlet chamber others of said guide ducts to said annular distributor chamber. with one of aid guide ducts. 9. A furnace as claimed in claim 7, further comprising a 8. A furnace as claimed in claim 7, further comprising cooling water supply pipe communicating with the bottom means in said tuyeres defining passages communicating the part of said annular distributor chamber. 

1. In a continuously tapped, acidically operated hot-blasT cupola furnace including a liningless stack, a water-cooled jacket surrounding said stack, tuyeres at the bottom of said stack, a hearth below the level of said tuyeres and a refractory lining in said hearth, the improvement comprising an inclined bottom in said hearth, at least two pressure siphons at a lower level than said bottom, means defining separate channels interconnecting said hearth and said pressure siphons, and means for cooling said tuyeres, said cooling means comprising doublewalled blast nozzles and coolant conducting means therewithin arranged to cool upper parts of said tuyeres more vigorously than lower parts thereof.
 2. A furnace as claimed in claim 1, further comprising a cover gastightly sealing each of said pressure siphons.
 3. A furnace as claimed in claim 1, wherein each tuyere is provided with one of said double-walled blast nozzles, a tip on said nozzle, cooling water supply pipes extending within the upper part of said nozzle and an outlet portion on each of said cooling water supply pipes, said outlet portions being adjacent said tip.
 4. A furnace as claimed in claim 3, wherein said outlet portions are directed outwards within said nozzle.
 5. A furnace as claimed in claim 3, wherein said nozzle contains four of said cooling water supply pipes and further comprising water outlet pipes interposed between said supply pipes.
 6. In a hot-blast cupola furnace including a liningless stack, a water-cooled jacket surrounding said stack, tuyeres at the bottom of said stack, a hearth below the level of said tuyeres and a refractory lining in said hearth, the improvement comprising an inclined bottom in said hearth, at least two pressure siphons at a lower level than said bottom, means defining separate channels communicating said hearth with said pressure siphons and means for cooling said tuyeres, said cooling means being arranged to cool upper parts of said tuyeres more vigorously than lower parts thereof, each of said tuyeres including a double-walled blast nozzle, a tip on said nozzle, axially extending walls within said nozzle subdividing said nozzle into guide ducts and means defining a passage within said tip interconnecting said guide ducts.
 7. A furnace as claimed in claim 6, further comprising means in each of said tuyeres defining an annular water distributor chamber, said chamber including means defining an outlet chamber at the top thereof, a water outlet pipe communicating with said outlet chamber and means within said tuyere defining a passage communicating said outlet chamber with one of aid guide ducts.
 8. A furnace as claimed in claim 7, further comprising means in said tuyeres defining passages communicating the others of said guide ducts to said annular distributor chamber.
 9. A furnace as claimed in claim 7, further comprising a cooling water supply pipe communicating with the bottom part of said annular distributor chamber. 